#include <iostream>
#include <stdio.h>
#include <vector>
#include <string>
#include <algorithm>
#include <functional>

#define REP(i,n) for(int i=0;i<n;i++)
#define maxi(a,b) (((a) > (b)) ? (a) : (b))
#define mini(a,b) (((a) > (b)) ? (a) : (b))
#define OUTL(a) cout << (a) << endl

using namespace std;

int main() {
	//cin.tie(0);
	//ios::sync_with_stdio(false);
	/********************************************************/
	int a;
	cin >> a;

	long long dp[50];
	dp[0] = 1;
	dp[1] = 1;
	for (int i = 2; i <= 50; i++) {
		dp[i] = dp[i - 1] + dp[i - 2];
	}

	cout << dp[a] << endl;
	/********************************************************/

	return 0;
}